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Abstract:

A shape memory polymer composition is described comprising greater that 90
wt. % cyclooctene, less than 10 wt. % of a multicyclic diene, comprising
at least two cyclo olefinic rings with at least two reactive double
bonds, and less than 2 wt. % of a metathesis catalyst.

Claims:

1. A polymerizable composition comprising:a) greater that 90 wt. %
cyclooctene,b) 0.1 to less than 10 wt. % of a multicyclic diene having at
least two cyclo olefinic rings with at least two reactive double bonds;c)
less than 2 wt. % of a metathesis catalyst; andd) optionally 5 wt. % or
less of an antioxidant;wherein said multicyclic diene is selected from
the group consisting of: ##STR00007## wherein X1 is a divalent
aliphatic group with 1 to 20 carbon atoms or an aromatic group;w is 0 or
1;X2 is a polyvalent aliphatic group having 1 to 20 carbon atoms or
an aromatic group;Y1 is a covalent bond or divalent functional group
selected from the group consisting of esters, amides, ethers, urethanes
and silanes;x is at least one, y may be zero, and x+y is 6 to 20, and z
is at least 2; or ##STR00008## whereinX3 is --O--, --S-- or
--NR1--, where R1 is H or C1-C4 alkyl,Y2 is a
polyvalent aliphatic group having 1 to 20 carbon atoms or an aromatic
group, optionally containing one or more Y1 groups, where Y1 is
a divalent functional group selected from the group consisting of esters,
amides, ethers, urethanes and silanes;z is at least 2, x is at least one,
y may be zero, and x+y is 6 to 20; or ##STR00009## whereinX1 is a
divalent aliphatic group having 1 to 20 carbon atoms or an aromatic
group;w is 0 or 1;X2 is a polyvalent aliphatic group having 1 to 20
carbon atoms or an aromatic group;Y1 is a covalent bond or divalent
functional group selected from the group consisting of esters, amides,
ethers, urethanes and silanes;and z is at least 2; or ##STR00010##
whereinX3 is --O--, --S-- or --NR1--, where R1 is H or
C1-C4 alkyl,Y2 is a polyvalent aliphatic group having 1 to
20 carbon atoms or an aromatic group, optionally containing one or more
Y1 groups, where Y1 is a covalent bond or divalent functional
group selected from the group consisting of esters, amides, ethers,
urethanes and silanes;z is at least 2, and ##STR00011## whereinv is at
least 1, w may be zero and v+w is 1-18.

4. The polymerizable composition of claim 1 comprising 0.1 to 5 wt. % of
an antioxidant.

5. The polymerizable composition of claim 1 comprising 0.5 to 3 wt. % of
an antioxidant.

6. The polymerizable composition of claim 1 wherein the metathesis
catalyst is a ruthenium carbene catalyst.

7. A crosslinked shape memory polymer comprising the reaction product of
the composition of claim 1.

8. The crosslinked shape memory polymer of claim 7 having an elastic
modulus of at least 90 MPa at 0.degree. C. and an elastic modulus of at
least 0.5 at 80.degree. C.

9. A method for preparing a shaped article comprising the step of casting
the composition of claim 1 into a mold and allowing it to cure.

10. The method of claim 9 further comprising the step of deforming the
shaped article at a temperature below the Tm.

11. The method of claim 9 further comprising the step of deforming the
article at a temperature above the Tm, then cooling the resulting
deformed article below the Tm to maintain the shape of the deformed
article.

12. The polymerizable composition of claim 1 comprising less than 3 wt. %
of a multicyclic diene having at least two cyclo olefinic rings with at
least two reactive double bonds.

13. The polymerizable composition of claim 1 wherein x+y is 6 to 10.

14. The polymerizable composition of claim 1 wherein said multicyclic
diene is the Diels-Alder adduct of a diacrylate with cyclopentadiene.

15. The polymerizable composition of claim 1 wherein said multicyclic
diene is the Diels-Alder adduct a cyclic diolefin and cyclopentadiene.

16. The polymerizable composition of claim 15 wherein said multicyclic
diene is the Diels-Alder adduct of 1,5-cyclooctadiene and
cyclopentadiene.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is a continuation-in-part of U.S. application Ser.
No. 12/339,502, filed Dec. 19, 2008, now pending, the disclosure of which
is incorporated by reference in their entirety herein.

[0003]Shape memory polymers (SMPs) have the unique ability to "remember" a
pre-set shape and, upon exposure to the appropriate stimuli, shift from a
deformed or altered shape back to the pre-set shape. Several commercially
important uses have been developed for shape memory polymers. For
example, shape memory polymers are commonly used in various medical,
dental, mechanical, and other technology areas for a wide variety of
products.

[0004]SMP's have a defined melting point (Tm) or glass transition
temperature (Tg). Above the Tm or Tg, the polymers are
elastomeric in nature, and are capable of being deformed with high
strain. The elastomeric behavior of the polymers results from either
chemical crosslinks or physical crosslinks (often resulting from
microphase separation). Therefore, SMP's can be glassy or crystalline and
can be either thermosets or thermoplastics.

[0005]The permanent shape of the SMP is established when the crosslinks
are formed in an initial casting or molding process. The SMP can be
deformed from the original shape to a temporary shape. This step is often
done by heating the polymer above its Tm or Tg and deforming
the sample, and then holding the deformation in place while the SMP
cools. Alternatively, in some instances the polymer can be deformed at a
temperature below its Tm or Tg and maintain that temporary
shape. Subsequently, the original shape is recovered by heating the
material above the melting point or glass transition temperature. The
recovery of the original shape, which is induced by an increase in
temperature, is called the thermal shape memory effect. Properties that
describe the shape memory capabilities of a material are the shape
recovery of the original shape and the shape fixity of the temporary
shape.

[0006]Shape memory polymers may be considered super-elastic rubbers; when
the polymer is heated to a rubbery state, it can be deformed under
resistance of about 1 MPa modulus, and when the temperature is decreased
below either a crystallization temperature or a glass transition
temperature, the deformed shape is fixed by the lower temperature
rigidity while, at the same time, the mechanical energy expended on the
material during deformation is stored. When the temperature is raised
above the transition temperature (Tm or Tg), the polymer will
recover to its original form as driven by the restoration of network
chain conformational entropy. The advantages of the SMPs will be closely
linked to their network architecture and to the sharpness of the
transition separating the rigid and rubber states. SMPs have an advantage
of high strain: to several hundred percent.

SUMMARY

[0007]The present disclosure provides a shape memory polymer composition
comprising greater that 90 wt. % cyclooctene, less than 10 wt. % of a
multicyclic diene, comprising at least two cyclo olefinic rings with at
least two reactive double bonds, and less than 2 wt. % of a metathesis
catalyst. In another aspect, the disclosure provides a shape memory
polymer comprising greater that 90 wt. % polymerized cyclooctene, and
crosslinked with less than 10 wt. % of a multicyclic olefin with at least
two cyclo olefinic rings with at least two reactive double bonds. In
another aspect, the present disclosure provides elastically deformed
shaped articles, which when heated above a transition temperature, will
elastically recover to an original form. Alternatively, the recovery of a
deformed shaped article may be effected by application of a low molecular
weight organic compound, such as a solvent, to act as a plasticizer.

[0008]In another embodiment, the disclosure provides a method of preparing
a shaped article comprising the steps of casting the shape memory polymer
composition into a mold and allowing it to cure. The resultant permanent
shape of the shaped article is the result of the crosslinking of the
cured polymer.

[0010]The shape polymer composition may be used in the preparation of any
shaped article in which it is advantageous for the article to elastically
recover an original shape when heated above a Tm. In some
embodiments the shape memory polymer composition may be cast into a
permanent shape and deformed to a temporary shape at a temperature below
the Tm so the deformed temporary shape is retained. Alternatively,
the shape memory polymer composition may be cast into a permanent shape,
deformed at a temperature above the Tm, and then cooled to a
temperature below the Tm so the deformed temporary shape is
retained. With either deformation method, when the deformed article is
heated above the Tm, or by exposure to solvent, the deformed article
will elastically recover the permanent shape.

[0013]In addition to cyclooctene, the shape memory polymer composition
comprises one or more multicyclic diene comprising at least two cyclo
olefinic rings with at least two reactive double bonds. This class of
shape-memory polymers depends on the crystalline domains and/or plastic
deformation of polycyclooctene to hold a temporary deformed shape, and
the polycyclooctene must be chemically crosslinked to hold a permanent
shape. The multicyclic diene crosslinking agent comprises at least two
cyclo olefinic rings with at least two reactive double bonds. The rings
may be fused or non-fused, spiro or bridging rings, and may be part of a
larger ring system. As used herein, double bonds of the cyclo olefinic
rings are considered reactive if they can undergo ring-opening metathesis
polymerization under typical reaction conditions as described herein.

[0014]Exemplary multifunctional polycyclic monomers include:

##STR00001##

With respect to the Formulas:X1 is a divalent aliphatic group with 1
to 20 carbon atoms or an aromatic group;X2 is a polyvalent,
preferably divalent aliphatic group with 1 to 20 carbon atoms or an
aromatic group;Y1 is a divalent functional group selected from the
group consisting of esters, amides, ethers, urethanes and silanes; and z
is at least 2, preferably 2;X3 is --O--, --S-- or --NR1--,
where R1 is H or C1-C4 alkyl,Y2 is a polyvalent,
preferably divalent aliphatic group with 1 to 20 carbon atoms or an
aromatic group, optionally containing one or more Y1 groups;z is at
least 2, preferably 2;x is at least one, y may be zero, and x+y is 6 to
20, preferably 6 to 10, andv is at least 1, w may be zero and v+w is
1-18, preferably 4 to 8. It will be understood that the substitution of
the ring may be at any non-vinylic carbon, as indicated in Formulas I and
II.

[0015]Other exemplary multicyclic dienes may include
tetracyclo[6,2,13,6,02,7]dodeca-4,9-diene, and alkyl derivatives
thereof. An example of a compound that falls within Formula III includes:

##STR00002##

[0016]Compounds of Formula I may be prepared by the following general
scheme:

##STR00003##

whereinY1* and Z are co-reactive functional groups that when combined
form the functional group Y1. Useful co-reactive functional groups
include hydroxyl, amino, carboxyl, isocyanato, ester and acyl halide
groups. Where the co-reactive functional group Y* is an isocyanato
functional group, the co-reactive functional group Z preferably comprises
a secondary amino or hydroxyl group. Where the co-reactive functional
group Y* comprises a hydroxyl group, the co-reactive functional group Z
preferably comprises a halide, carboxyl, isocyanato, ester, or acyl
halide group. Where the co-reactive functional group Y* comprises a
carboxyl, ester, or acyl halide group, the co-reactive functional group Z
preferably comprises a hydroxyl, amino, epoxy, isocyanate, or oxazolinyl
group. Most generally, the reaction is between nucleophilic and
electrophilic functional groups that react by a displacement or
condensation mechanism.

[0017]Compounds of formulas II to IV may be similarly prepared. In some
embodiments, compounds of Formula III may be prepared by a Diels-Alder
cycloaddition of a diacrylate with cyclopentadiene. Compounds of Formula
V may be generally prepared by a Diels-Alder cycloaddition reaction
between a cyclic diolefin and cyclopentadiene. Other reaction schemes
will be apparent to one skilled in the art.

[0018]In general, the shape memory polymers disclosed herein comprise one
or more polymers prepared by ring opening metathesis polymerization of
cyclooctene and one or more multicyclic dienes catalyzed by olefin
metathesis catalysts; see for example, K. J. Ivin, "Metathesis
Polymerization" in J. I. Kroschwitz, ed., Encyclopedia of Polymer Science
and Engineering, Vol. 9, John Wiley & Sons, Inc., U.S.A., 1987, p. 634.
Metathesis polymerization of cycloalkene monomers typically yields
polymers having an unsaturated linear backbone. The degree of
unsaturation of the repeat backbone unit of the polymer is the same as
that of the monomer. For example, with cyclooctene and the compound of
Formula II, in the presence of an appropriate catalyst, the resulting
polymer may be represented by:

##STR00004##

where a and b are the molar percents of the polymerized monomers. As shown
by the above reaction, metathesis polymerization of cyclooctene and a
multicyclic diene can result in a crosslinked polymer. The degree of
unsaturation of the repeat backbone unit of the polymer is the same as
that of the monomers. With respect to the above scheme, it will be
understood that the resulting polymer may further contain monomer units
resulting from the metathesis of just one of the reactive double bonds of
the multicyclic diene; i.e. the resulting polymer may contain:

##STR00005##

where c has a non-zero value and a+(b+c) is the fraction of polymerized
monomers. Because the second double bonds of some multicyclic dienes,
such as dicyclopentadiene or norbornadiene, are less reactive in a
metathesis reaction, different amounts are generally required to produce
sufficient amounts of crosslinking. Also, some multicyclic dienes, such
as dicyclopentadiene disrupt crystallinity of the cyclooctene more than
others, and must therefore be used at lower levels to maintain a
sufficient modulus below the Tm; i.e. less than 3 wt. %.

[0019]The multicyclic diene may crosslink the cyclooctene polymer as
described above. The degree to which crosslinking occurs depends on the
relative amounts of different monomers and on the conversion of the
reactive groups in those monomers, which in turn, is affected by reaction
conditions including time, temperature, catalyst choice, and monomer
purity. The multicyclic diene is used in amount such that the polymer is
crosslinked, and the difference in elastic modulus of the polymer between
0° C. and 80° C. is maximized. Preferably, the elastic
modulus of the polymer at 0° C. is at least 90 MPa and the elastic
modulus at 80° C. is at least 0.5 MPa. Generally the multicyclic
diene is used in amounts of 0.1 to less than 10 wt. % of the polymer
composition, preferably less than 5%, more preferably less than 3 wt. %.

[0020]The degree of crosslinking affects the modulus of the shape memory
polymer above the Tm. If the crosslinking density is too high, the
polymer breaks at relatively low levels of elongation. With no
crosslinking, the polymer may yield at high temperature and display poor
shape-memory properties.

[0022]In some embodiments, the monomer composition comprises a metathesis
catalyst system comprising a compound of the formula:

##STR00006##

wherein:

[0023]M is selected from the group consisting of Os and Ru;

[0024]R and R1 are independently selected from the group consisting
of hydrogen and a substituent group selected from the group consisting of
C1-C20 alkyl, C2-C20 alkenyl, C2-C20
alkoxycarbonyl, aryl, C1-C20 carboxylate, C1-C20
alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy and
aryloxy; the substituent group optionally substituted with a moiety
selected from the group consisting of C1-C5 alkyl, halogen,
C1-C5 alkoxy and phenyl; the phenyl optionally substituted with
a moiety selected from the group consisting of halogen, C1-C5
alkyl, and C1-C5 alkoxy;

[0025]X and X1 are independently selected from any anionic ligand;
and

[0026]L and L1 are independently selected from any phosphine of the
formula --PR3R4R5, wherein R3 is selected from the
group consisting of neophyl, secondary alkyl and cycloalkyl and wherein
R4 and R5 are independently selected from the group consisting
of aryl, neophyl, C1-C10 primary alkyl, secondary alkyl, and
cycloalkyl. L and L1 are also independently selected from
imidazol-2-ylidine, and dihydroimidazol-2-ylidine groups.

[0027]The metathesis catalyst system may also comprise a transition metal
catalyst and an organoaluminum activator. The transition metal catalyst
may comprise tungsten or molybdenum, including their halides, oxyhalides,
and oxides, such as WCl6. The organoaluminum activator may comprise
trialkylaluminums, dialkylaluminumhalides, or alkylaluminumdihalides.
Organotin and organolead compounds may also be used as activators, for
example, tetraalkyltins and alkyltinhydrides may be used.

[0028]The choice of particular catalyst system and the amounts used may
depend on the particular amounts of monomers being used, as well as on
desired reaction conditions, desired rate of cure, and so forth. In
particular, it is be desirable to include the above-described osmium and
ruthenium catalysts in amounts of from about 0.001 to about 2.0 wt. %,
preferably about 0.01 to 0.5 wt. %, relative to the total weight of the
cyclooctene and multicyclic diene.

[0029]Both the WCl6 catalyst precursor and the
(C2H5)2AlCl activator are sensitive to ambient moisture
and oxygen, so it is preferable to maintain the reactive solutions under
inert conditions. Once mixed, the catalyst solution may be injected into
an air-filled mold as long the polymerization is rapid and exposure to
air is minimized. Preferably, the mold can be purged with an inert gas
such as nitrogen before introducing the monomer composition. The
polymerization can occur at room temperature, or heat can be used to help
accelerate the polymerization.

[0030]The monomer composition may comprise additional optional components.
For example, if the metathesis catalyst system comprises
WCl6/(C2H5)2AlCl, then water, alcohols, oxygen, or
any oxygen-containing compounds may be added to increase the activity of
the catalyst system as described in Ivin. Other additives can include
chelators, Lewis bases, plasticizers, inorganic fillers, and
antioxidants, preferably phenolic antioxidants.

[0031]In the catalyst solution, the WCl6 catalyst precursor may cause
the polymerization of the monomer before being mixed with the
organoaluminum or organotin activator solution. To prevent this premature
polymerization, a chelator or Lewis base stabilizer can be added to the
WCl6 solution as taught in U.S. Pat. No. 4,400,340 (Klosiewicz et
al). Particularly preferred stabilizers are 2,4-pentanedione or
benzonitrile. This can be added at 50 mol % to 300 mol % and more
preferably from 100 mol % to 200 mol % relative to the WCl6.

[0032]It is also taught in U.S. Pat. No. 4,400,340 (Klosiewicz et al) that
the addition of a Lewis base to the activator solution can slow the
gelation of the mixed monomer composition, thus allowing increased
working time. One preferred Lewis base for this purpose is butyl ether.
Another preferred Lewis base moderator which is beneficial in that it can
be polymerized into the shape memory polymer is
norborn-2-ene-5-carboxylic acid butyl ester. The Lewis base moderator can
be included from about 0 mol % to 500 mol %, and more preferably from 100
mol % to 300 mol % relative to the organoaluminum or organotin activator.

[0033]Additionally, a halogen-containing additive can be included to
increase conversion of monomer during the polymerization, as taught in
U.S. Pat. No. 4,481,344 (Newburg et al). This halogen-containing compound
can be included from 0 mol % to 5000 mol %, and preferably from 500 mol %
to 2000 mol % all relative to the WCl6. A particularly preferable
halogen containing additive is ethyl trichloroacetate.

[0034]To produce a shaped article from the shape memory polymer
composition, it is desirable that no solvent be included in the
formulations. If solvent is used to help initially dissolve some
component of the catalyst system, such as the WCl6, it is desirable
to remove the solvent under vacuum before polymerizing the mixture.

[0035]Preferably, the catalyst is selected from
benzylidenebis(tricyclohexylphosphin) dichlororuthenium (Grubbs I
catalyst) or
Benzyliden[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinyliden]dichloro(t-
ricyclohexylphosphin)ruthenium (Grubbs II catalysts). Reference may be
made to U.S. Pat. Nos. 5,831,108 and 6,111,121 (Grubbs et al.). Solvent
is not normally removed from the Grubbs I and II catalysts, due to their
rapid reactivity in the presence of the monomers.

[0036]Other additives can include plasticizers, organic or inorganic
fillers, and antioxidants, preferably phenolic antioxidants. Any such
additional additives should be used in amounts such that the
crystallinity of the shape memory polymer is maintained. Generally such
additives are used in amounts of less that 5 wt. %, relative to the total
amount of the shape memory polymer composition.

[0037]Shaped articles can be prepared from the shape memory polymer
compositions by any suitable technique used for thermoset polymers. The
articles may be cast into a suitable mold and cured, or injection molded,
such as by reaction injection molding (RIM) whereby the polymer
composition is injected into a mold and cured.

[0038]The mold may be flexible or rigid. Useful materials that may be used
to make the mold include metal, steel, ceramic, polymeric materials
(including thermoset and thermoplastic polymeric materials), or
combinations thereof. The materials forming the mold should have
sufficient integrity and durability to withstand the particular monomer
compositions to be used as well as any heat that may be applied thereto
or generated by the polymerization reaction. In some embodiments, the
mold may comprise an injection mold. In this case, the mold may comprise
two halves which mate together. For injection molding, the monomer
composition may be injected via an injection port into a cavity or
cavities of the mold, and there is typically some output port for air,
nitrogen, etc. to escape. Filling of the cavity may be facilitated by
vacuum attached via the output port.

[0039]To prepare a shaped article having a shape memory, the article can
be molded and crosslinked to form a permanent shape. If the article
subsequently is formed into a second shape by deformation, the object can
be returned to its original shape by heating the object above the
Tm. In other embodiments, a solvent such as alkyl alcohol, acetone,
etc. can partially dissolve or plasticize the crystalline phase and cause
the same recovery.

[0040]The original shaped article, having a first permanent shape, may
then be deformed by either of two methods. In the first, the shaped
article, as molded, is heated above the Tm or Tg, deformed to
impart a temporary shape, then cooled below the Tm or Tg to
lock in the temporary shape. In the second, the shaped article is
deformed at a temperature below the Tm or Tg by the application
of mechanical force, whereby the shaped article assumes a second
temporary shape through forced deformation; i.e. cold drawing. When
significant stress is applied, resulting in an enforced mechanical
deformation at a temperature lower than the Tm or Tg, strains
are retained in the polymer, and the temporary shape change is
maintained, even after the partial liberation of strain by the elasticity
of the polymer.

[0041]The shaped article may be deformed in one, two or three dimensions.
All or a portion of the shaped article may be deformed by mechanical
deformation. The shaped article may be deformed by any desired method
including embossing, compression, twisting, shearing, bending, cold
molding, stamping, stretching, uniformly or non-uniformly stretching, or
combinations thereof.

[0042]The original or permanent shape is recovered by heating the material
above the Tm whereby the stresses and strains are relieved and the
material returns to its original shape. The original or permanent shape
of the shaped article can be recovered using a variety of energy sources.
The composition can be immersed in a heated bath containing a suitable
inert liquid (for example, water or a fluorochemical fluid) that will not
dissolve or swell the composition in either its cool or warm states. The
composition can also be softened using heat sources such as a hot air
gun, hot plate, conventional oven, infrared heater, radiofrequency
(Rf) sources or microwave sources. The composition can be encased in
a plastic pouch, syringe or other container which is in turn heated (e.g.
electrically), or subjected to one or more of the above-mentioned heating
methods. Alternatively, the original shape of the deformed article may be
recovered by exposure to a low molecular weight organic compound, such as
a solvent, which acts as a plasticizer. The low molecular weight organic
compound diffuses into the polymer bulk, triggering the recovery by
disrupting the crystallinity of the crosslinked polycyclooctene.

[0043]In some embodiments, it may be desirable to recover only a portion
of the shaped article. For example, heat and/or solvent can be applied to
only a portion of the deformed surface of the substrate to trigger the
shape memory recovery in these portions only.

[0044]In one embodiment, the shaped article may comprise a heating
element, such as a resistive heating element encapsulated thereby. After
deformation, the resistive heating element may be connected to a source
of electricity imparting heat to the bulk of the polymer, which raises
the temperature above the Tm so the deformed article assumes the
original permanent shape.

[0045]In other embodiments, the heating step may be an indirect heating
step whereby the deformed polymer is warmed by irradiation, such as
infrared radiation. As the responsiveness of the shape memory polymer is
limited by the heat capacity and thermal conductivity, the heat transfer
can be enhanced by the addition of conductive fillers such as conductive
ceramics, carbon black and carbon nanotubes. Such conductive fillers may
be thermally conductive and/or electrically conductive. With electrically
conductive fillers, the polymer may be heated by passing a current
therethough. In some embodiments, the shape memory polymer may be
compounded with conductive fillers, and the polymer heated inductively by
placing it in an alternating magnetic field to induce a current.

[0047]The polymer compositions can be formed into the shape of an implant
which can be implanted within the body to serve a mechanical function.
Examples of such implants include rods, pins, screws, plates and
anatomical shapes. A particularly preferred use of the compositions is to
prepare sutures that have a rigid enough composition to provide for ease
of insertion, but upon attaining body temperature, soften and form a
second shape that is more comfortable for the patient while still
allowing healing.

[0049]In some embodiments, the shaped articles are fasteners, including
grommets and rivets. A rivet may comprise a longitudinally-deformed
shaped cylinder that may be inserted into an object or workpiece having
an aperture therethrough. Upon heating, the deformed cylinder will
contract longitudinally and expand laterally. The radii of the permanent
and deformed shapes of the fastener are chosen such that the fastener may
be inserted into the workpiece, but will expand to fill and grip the
workpiece. Further, the degree of longitudinal deformation (stretching)
of the fastener may be chosen such that the fastener will impart
compression to the workpiece on heat recovery to the permanent shape.

[0051]This monomer was prepared using a procedure similarly described in
patent GB 1312267 (1973). A mixture of 1,5-cyclooctadiene (201.2 g, 1.86
mol, Aldrich) and dicyclopentadiene (18.5 g, 0.14 mol, Aldrich) were
placed in a 1 L stainless steel Parr vessel. The reactor was sealed and
placed placed in an oven at 210° C. for 50 hours. The vessel was
cooled, and the contents were distilled. Excess cyclooctadiene was
removed at 35-40° C. @ 10 mmHg pressure. The remaining oil was
distilled and a colorless fraction was collected at 60-75° C. @ 1
mmHg (26.373 g). This crude product was redistilled and a fraction was
collected at 57-60° C. @ 1 mmHg (14.08 g).

Preparative Example 2

T-NB

[0052]Cyclopentadiene was obtained from dicyclopentadiene (Aldrich) by
heating 140 g of dicyclopentadiene at 175° C. for 6 hours and
collecting the distillate. 90 g of the freshly prepared cyclopentadiene
was slowly added to a dried round bottom flask with 175 g of
tricyclodecane dimethanol diacrylate (Aldrich). This solution was stirred
at 55° C. for 20 hours, after which, excess cyclopentadiene was
removed under vacuum (0.2 Ton for 4 hours). The resulting tricyclodecane
dinorbornene (TCDDN) was used without further purification.

Test Methods:

DMA:

[0053]DMA experiments were performed in tensile mode on a TA Q800 Dynamic
Mechanical Analyzer. Test samples were strips of material nominally 1 mm
thick and 6 mm wide. The amplitude was maintained at 10 microns, the
frequency was 1 Hz, and the ramp rate was 3° C./min.

Shape Memory Polymer Characterization:

[0054]Shape-memory performance was evaluated through a tensile
strain-recovery protocol. A strip of polymer was loaded into the tensile
clamps of a TA Q800 DMA. The test strip was about 6.0 to 6.4 mm in width,
0.55 to 0.96 mm in thickness and about 20 mm in length. The material was
then equilibrated at a temperature above the Tm ("Fixing
Temperature"). A static force was applied to produce a strain in the
range of 20%-100%. This static force was held constant as the material
was then cooled to well below its Tm. The force was then relaxed and
the temperature was ramped through the Tm while monitoring the
strain recovery of the material. The recovered strain was defined as
1-(final strain-initial strain)/(peak strain-initial strain). The range
of temperature over which the strain was recovered is characterized by
the temperature at which the 20% of the strain recovery was complete and
the temperature at which 80% of the strain recovery was complete. In some
cases, the material was then immediately subjected to additional cycles
of the strain-recovery testing. (In repeated cycles, the initial strain
is defined as the final strain from the previous cycle.)

Examples 1-5 and Comparative Examples 1-3

[0055]Grubbs II catalyst dissolved in toluene was added to the monomer
solution containing cyclooctene and the multicyclic diene in the amounts
shown in Table 1. Antioxidant, if used, was dissolved in the monomers.
This mixture was then cast into a glass channel that was 1 mm deep, 25 mm
wide, and between 30 and 40 mm long. The channel was then covered with
glass. The samples were allowed to cure for 30 min at RT followed by 60
min at 100° C. Table 1 shows the formulations of crosslinked
polymers that were prepared and tested.

[0056]As can be seen in Table 1, with no additives, the modulus is
relatively high at 0° C., (Comparative Ex. 1) but as either
antioxidant (Comparative examples 2 and 3) or crosslinkers are added, the
modulus at 0° C. drops. It is expected that additives should
disrupt the ability of the polymer to crystallize.

[0057]The degree of crosslinking affects the modulus above the melting
point (20-60° C.). With no crosslinking, the sample yields at high
temperature and does not display shape-memory (comparative examples 1, 2,
and 3).

[0058]The shape-memory characteristics of the crosslinked pCOE samples are
shown in Table 2. The ratio of the peak stress and peak strain gives a
general indication of the stiffness of the material above the melting
point. A high stiffness in this rubbery region should correspond to high
recovery force. A combination of high elongation and high stiffness
should correspond to the greatest amount of potential energy available to
do work during the recovery step of a shape-memory cycle.

[0059]FIGS. 1 and 2 show a force-strain plot and a strain-temperature plot
for the polymer of Example 3. FIG. 1 is a Force-Strain plot showing the
initial deformation step followed by cooling while under constant applied
load. FIG. 2 is a Strain-Temperature plot showing the initial deformation
step above the melting temperature followed by cooling while under the
static load, and then the recovery step of heating the sample with no
applied load. The range of temperatures over which this strain is
recovered remains fairly constant with the different formulations
(46° C. to 57° C.).